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One year ago, the idea that microbes might cause obesity gained a foothold when the Pennington Biomedical Research Center in Louisiana created the nation’s first department of viruses and obesity. It is headed by Nikhil Dhurandhar, a physician who invented the term “infectobesity” to describe the emerging field. Dhurandhar’s particular interest is in the relationship between obesity and a common virus, the adenovirus. Other scientists, led by a group of microbiologists at Washington University in St. Louis, are looking at the actions of the trillions of microbes that live in everyone’s gut, to see whether certain intestinal microbes may be making their hosts fat.

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Of the trillions and trillions of cells in a typical human body — at least 10 times as many cells in a single individual as there are stars in the Milky Way — only about 1 in 10 is human. The other 90 percent are microbial. These microbes — a term that encompasses all forms of microscopic organisms, including bacteria, fungi, protozoa and a form of life called archaea — exist everywhere. They are found in the ears, nose, mouth, vagina, anus, as well as every inch of skin, especially the armpits, the groin and between the toes. The vast majority are in the gut, which harbors 10 trillion to 100 trillion of them. “Microbes colonize our body surfaces from the moment of our birth,” Gordon said. “They are with us throughout our lives, and at the moment of our death they consume us.”

Known collectively as the gut microflora (or microbiota, a term Gordon prefers because it derives from the Greek word bios, for “life”), these microbes have a Star Trek analogue, he says: the Borg Collective, a community of cybernetically enhanced humanoids with functions so intertwined that they operate as a single intelligence, sort of like an ant colony. In its Borglike way, the microflora assumes an extraordinary array of functions on our behalf — functions that we couldn’t manage on our own. It helps create the capillaries that line and nourish the intestines. It produces vitamins, in particular thiamine, pyroxidine and vitamin K. It provides the enzymes necessary to metabolize cholesterol and bile acid. It digests complex plant polysaccharides, the fiber found in grains, fruits and vegetables that would otherwise be indigestible.

And it helps extract calories from the food we eat and helps store those calories in fat cells for later use — which gives them, in effect, a role in determining whether our diets will make us fat or thin.

In the womb, humans are free of microbes. Colonization begins during the journey down the birth canal, which is riddled with bacteria, some of which make their way onto the newborn’s skin. From that moment on, every mother’s kiss, every swaddling blanket, carries on it more microbes, which are introduced into the baby’s system.

By about the age of 2, most of a person’s microbial community is established, and it looks much like any other person’s microbial community. But in the same way that it takes only a small percentage of our genome to make each of us unique, modest differences in our microflora may make a big difference from one person to another. It’s not clear what accounts for individual variations. Some guts may be innately more hospitable to certain microbes, either because of genetics or because of the mix of microbes already there. Most of the colonization probably happens in the first few years, which explains why the microflora fingerprints of adult twins, who shared an intimate environment (and a mother) in childhood, more closely resemble each other than they do those of their spouses, with whom they became intimate later in life.

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I had no idea that we had that much in the way of microbes in our bodies. Of course I knew that they helped digest food and whatnot, but I didn't know the extent of what they did.

The article is long - it runs for 7 pages and I'm not quite done - but it sure makes for interesting reading. I'm sure learning a lot.

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“And we documented that fat people do eat too much — our subjects ate an average of 6,700 calories a day. But what was so impressive to me was the fact that not all fat people eat too much.”

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If Ad-36 is a cause of obesity, Atkinson says, you’re more likely to catch it from a newly infected and still-contagious thin person than from someone who has already gained weight because of its effects.

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Of the trillions and trillions of cells in a typical human body — at least 10 times as many cells in a single individual as there are stars in the Milky Way — only about 1 in 10 is human. The other 90 percent are microbial.

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